Preparation of coated iron powders by chemical plating

Small iron particles can be produced by reduction of γ-Fe
2
O
3
and α-FeOOH with hydrogen; they show outstanding magnetic properties and can be used for recording media. The main difficulty concerns the tendency of these particles to oxidize. We have studied a preparation process in two steps: a) reduction of iron oxides or oxy-hydroxides; b) chemical plating in the same furnace. The magnetic properties of the iron powders chiefly depend on the reduction step. The water content in the gas leaving the furnace has been shown to be the main parameter determining the obtainment of powders with high magnetic properties. The iron powders, which were pyrophoric, have been quenched in chemical plating bath of suitable formulation and coated with cobalt or copper. Typical magnetic properties are: saturation magnetization σ
sat
= 130-165 emu/g, intrinsic coercivity
j
H
c
= 350-450 Oe; best magnetic properties: σ
sat
=155 emu/g,
j
H
c
=700 Oe. The coated powders have been submitted to heat treatment in air saturated with water, showing a good resistance to oxidation.